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Hematotoxicological And Mosquito Larvicidal Studies Of Crystal Proteins Secreted By Bacillus Thuringiensis And Bacillus Sphaericus

ABSTRACT

In Nigeria, mosquitos are transmitting several important human disease etiological agents, including malaria, and causing thousand of death every year. Mosquito control is based mostly on chemical insecticides which may be toxic and cause environmental deprivation. The objective of this study is to evaluate the hematological and larvicidal potentials of Bacillus thuringiensis and Bacillus sphaericus isolated from the soil. A total of fifty soil samples from garden soil were collected and screened for the presence of Bacillus thuringiensis and Bacillus sphaericus using pour plate technique. The organisms obtained from mixed culture plates were characterized and identified using their morphological, biochemical and molecular characteristics. Oral administration of the bacteria crystal proteins (Cry) and examination of blood samples from the experimental mice were carried out to assess the effect of the crystal proteins on the hematological indices of the mice. Larvicidal activities of the Cry were carried out by exposing the third instars’ of larva stage of Anopheles gambiae to different concentrations (12.50, 25.00, 50.00, 100.00 and 200.00 ppm) of the Cry. The study revealed the presence of Bacillus sphaericus strain D45 (BsD45), Bacillus sphaericus strain DSM396 (BsDSM396), Bacillus thuringiensis strain DX3 (BtDX3) and Bacillus thuringiensis strain WO15 (BtWO15). The maximum spore counts (3.71 logCfu/ml) and Cry (22.03 mg/L) were revealed from BtDX3 after 96 h. There was no significant (p> 0.05) effect of the crystal proteins on the hematological indices of the mice, but slight deviations were observed in the lymphocytes, neutrophils and total white blood cells (WBCs). There was pronounced larvicidal activities of the Cry, mostly from BtDX3 and BtWO15 and these increased significantly (p< 0.05) as the concentrations of the Cry increased. The LC₅₀ of the study revealed significant (p< 0.05) activities of the crystal proteins against the mosquito larvae, of which the Cry from BtDX3 showed the most pronounced activity. Therefore the Cry secreted from the BsD45, BsDSM396, BtDX3 and BtWO15 showed slight deviation only on the WBCs, lymphocytes and neutrophils. There were significant larvicidal activities of the Cry, of which Cry from strains of Bacillus thuringiensis (Bt) especially BtDX3 recorded the most pronounced activity.

Key words: Bacillus thuringiensis, hematological indices, Bacillus sphaericus. larvicidal potentials.